1. Field of the Invention
The present invention relates to a semiconductor package.
2. Description of the Related Art
A conventional semiconductor package comprises a base plate formed of a material high in thermal conductivity, for example, copper or copper alloy, and having a flat first surface and a flat second surface facing in the opposite direction to the first surface, and a semiconductor element mounted in a predetermined region on the flat first surface of the base plate. The second surface of the base plate is supported in a predetermined position on a supporting member. The supporting member is also made of a metal material relatively high in thermal conductivity, but not so high as that of the base plate, such as aluminum or iron.
The semiconductor element includes a semiconductor substrate made of, for example, silicon and mounted in the predetermined region on the first surface of the base plate, a heat generating unit disposed or formed on the semiconductor substrate and generating a relatively large quantity of heat by operation like, for example, an integrated circuit, and various circuit units disposed or formed around the heat generating unit on the semiconductor substrate. The various circuit units include printed wirings electrically connected to the heat generating unit and generate only very small quantity of heat as compared with the heat generated by the heat generating unit in operation. The various circuit units include a plurality of external connection terminals projecting from the printed wirings and the first surface of the base plate.
The predetermined region on the first surface of the base plate is surrounded by a frame member, and an opening of the frame member on the opposite side of the first surface is closed by a lid. The plurality of external connection terminals of the semiconductor element penetrate through the frame member and are exposed to an external space.
When electric signals are input to the plurality of external connection terminals of the semiconductor element, the heat generating unit and various circuit units of the semiconductor element operate and generate heat. The heat is radiated to an external space through a region excluding the second surface on the outer surface of the base plate or is diffused to the supporting member through the second surface of the base plate.
Along with the recent trend in which the performance of the semiconductor element becomes higher, the quantity of heat generated in the heat generating unit is increasing steeply. The semiconductor element cannot exhibit its predetermined performance when its temperature exceeds a predetermined value. Recently, therefore, the base plate is provided with various cooling measures in order to enhance the heat radiation effect from the base plate.
These conventional various cooling measures includes, for example, a direct attachment of a heat sink having a plurality of cooling fins to the second surface of the base plate or a combination of a high heat conductive element of a material having a higher thermal conductivity than that of the base plate, such as a graphite sheet, and adhered to the second surface and the heat sink additionally mounted on the high heat conductive element. The graphite sheet combined with the heat sink and adhered to the second surface is disclosed in, for example, Japanese Patent Application KOKAI Publication No. 2004-288949.
In such conventional cooling measures, the heat generated by the heat generating unit of the semiconductor element on the first surface is transferred to the second surface in the base plate, and is positively discharged from the second surface by means of the heat sink.
Considering, however, the present development scene of semiconductor elements, that is, the degree of increasing of heat density caused by progress of performance and reduction of outer size, it is desired to develop cooling measures having higher cooling performance than that of the conventional cooling measures for ensuring the predetermined high performance of recent advanced semiconductor elements.